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Determine the chemical formula of magnesium chloride.

Chemistry

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Answer

2.1×1022\text{2.1} \times 10^{22}

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here's the solution for question 3:

Question 3: How many chloride ions are present in 1.7g1.7 \text{g} of magnesium chloride crystals? (Avogadro's constant = 6.0×10236.0 \times 10^{23}, Mg = 24, Cl = 35.5)

  1. Determine the chemical formula of magnesium chloride.

    Magnesium is a Group 2 element, forming Mg2+\text{Mg}^{2+} ions. Chlorine is a Group 17 element, forming Cl−\text{Cl}^{-} ions. To balance the charges, the formula for magnesium chloride is MgCl2\text{MgCl}_2.

  2. Calculate the molar mass of magnesium chloride (MgCl2\text{MgCl}_2).

    Given atomic masses: Mg = 24, Cl = 35.5

    Molar mass of MgCl2=Molar mass of Mg+(2×Molar mass of Cl)\text{Molar mass of MgCl}_2 = \text{Molar mass of Mg} + (2 \times \text{Molar mass of Cl}) Molar mass of MgCl2=24 g/mol+(2×35.5 g/mol)\text{Molar mass of MgCl}_2 = 24 \text{ g/mol} + (2 \times 35.5 \text{ g/mol}) Molar mass of MgCl2=24 g/mol+71 g/mol=95 g/mol\text{Molar mass of MgCl}_2 = 24 \text{ g/mol} + 71 \text{ g/mol} = 95 \text{ g/mol}

  3. Calculate the moles of magnesium chloride in 1.7g1.7 \text{g}.

    Given mass of MgCl2=1.7 g\text{MgCl}_2 = 1.7 \text{ g}

    Moles of MgCl2=MassMolar mass\text{Moles of MgCl}_2 = \frac{\text{Mass}}{\text{Molar mass}} Moles of MgCl2=1.7 g95 g/mol≈0.01789 mol\text{Moles of MgCl}_2 = \frac{1.7 \text{ g}}{95 \text{ g/mol}} \approx 0.01789 \text{ mol}

  4. Calculate the number of MgCl2\text{MgCl}_2 formula units.

    Using Avogadro's constant (6.0×10236.0 \times 10^{23} formula units/mol):

    Number of MgCl2 units=Moles×Avogadro’s constant\text{Number of MgCl}_2 \text{ units} = \text{Moles} \times \text{Avogadro's constant} Number of MgCl2 units=0.01789 mol×6.0×1023 units/mol\text{Number of MgCl}_2 \text{ units} = 0.01789 \text{ mol} \times 6.0 \times 10^{23} \text{ units/mol} Number of MgCl2 units≈0.10734×1023=1.0734×1022 units\text{Number of MgCl}_2 \text{ units} \approx 0.10734 \times 10^{23} = 1.0734 \times 10^{22} \text{ units}

  5. Calculate the number of chloride ions.

    From the formula MgCl2\text{MgCl}_2, each formula unit contains 2 chloride ions (Cl−\text{Cl}^{-}).

    Number of Cl− ions=2×Number of MgCl2 units\text{Number of Cl}^{-} \text{ ions} = 2 \times \text{Number of MgCl}_2 \text{ units} Number of Cl− ions=2×1.0734×1022\text{Number of Cl}^{-} \text{ ions} = 2 \times 1.0734 \times 10^{22} Number of Cl− ions=2.1468×1022\text{Number of Cl}^{-} \text{ ions} = 2.1468 \times 10^{22}

    Rounding to two significant figures (due to 1.7g1.7 \text{g}), we get:

    Number of Cl− ions=2.1×1022\text{Number of Cl}^{-} \text{ ions} = 2.1 \times 10^{22}

    The number of chloride ions present is 2.1×1022\text{2.1} \times 10^{22}.

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